Genetics - Unit Ass. 1

Allele

A variant form of a gene at a specific locus on a chromosome, inherited from each parent.

Autosomal

Refers to genes located on autosomes, which are non-sex chromosomes; humans have 22 pairs of autosomes.

Barr Bodies

Inactivated X chromosomes found in female mammalian cells for dosage compensation.

Blending Inheritance

An outdated theory that offspring traits result from a mix of parental traits, rather than distinct gene inheritance.

Centimorgan (cM)

A unit of genetic map distance representing a 1% recombination frequency between two loci.

Centromere

The region of a chromosome where sister chromatids are joined.

Chiasma

The physical site where homologous chromosomes exchange genetic material during crossing over.

Chi-square Test

A statistical test used to compare observed and expected ratios in genetics.

Degrees of Freedom (df)

Calculated as number of categories minus one.

Critical Values

Values used in chi-square tests to determine statistical significance.

Sister Chromatids

Identical copies of a chromosome, connected at the centromere.

Non-sister Chromatids

Chromatids from homologous chromosomes that can exchange genetic material.

Chromosome

A DNA molecule containing genetic information; humans have 46 chromosomes.

Coefficient of Coincidence

A measure of how often double crossovers occur compared to expected frequency.

Cohesin

A protein that holds sister chromatids together until they separate.

Complementation

A genetic test where mutations in different genes are combined to see if they restore a wild-type phenotype.

Crossing Over

The exchange of genetic material between homologous chromosomes during meiosis.

Diploid (2n)

A cell containing two sets of chromosomes, one from each parent.

Complete Dominance

One allele completely masks the effect of another.

Incomplete (Partial) Dominance

Heterozygotes show an intermediate phenotype.

Co-dominance

Both alleles are fully expressed in heterozygotes.

Dosage Compensation

Mechanism that equalizes gene expression between sexes.

Double Crossover (DCO)

Two crossover events between homologous chromosomes during meiosis.

Epistasis

When one gene affects or masks the expression of another gene.

Forked-line Diagram

A method used to predict genetic outcomes using branching pathways.

Gamete

A haploid reproductive cell carrying one set of chromosomes.

Gene

A DNA sequence that codes for a protein or functional RNA.

Gene-environment Interaction

When environmental factors influence gene expression.

Genetic Linkage

The tendency of genes located close together on a chromosome to be inherited together.

Genotype

The genetic makeup of an organism.

Germline

Cells that lead to gametes; mutations are heritable.

Haploid (1n)

A cell with one set of chromosomes.

Haplosufficiency

When a single functional allele is enough to maintain a normal phenotype.

Hemizygous

Having only one allele for a gene, as in males for X-linked genes.

Homozygous

Having two identical alleles.

Heterozygous

Having two different alleles.

Incomplete Penetrance

When individuals with a genotype do not always express the expected phenotype.

Interference

One crossover event reduces the likelihood of another occurring nearby.

Kinetochore

A protein complex on the centromere where spindle fibers attach.

Map Unit (m.u.)

Another term for a centimorgan, measuring genetic distances.

Mendel’s Law of Segregation

Each individual has two alleles for a gene, which separate during gamete formation.

Mendel’s Law of Independent Assortment

Genes on different chromosomes assort independently during meiosis.

Meiosis

Cell division that reduces chromosome number by half, producing gametes.

Mitosis

Cell division producing identical daughter cells.

Monohybrid Cross

A cross involving one gene.

Dihybrid Cross

A cross involving two genes.

Multiplication Rule

Probability of independent events occurring together.

Addition Rule

Probability of mutually exclusive events.

Mutation

A change in DNA sequence that may affect gene function.

Mutant

An organism or allele carrying a mutation.

Non-disjunction

Failure of chromosomes to separate properly during cell division.

Pangenesis

A discredited hypothesis that genetic information is passed through body cells.

Parental Gametes

Gametes with the same allele combination as parents.

Recombinant Gametes

Gametes with new allele combinations due to crossing over.

Particulate Theory

Mendel’s concept that traits are inherited as discrete units.

Pedigree

A chart used to analyze inheritance patterns.

Phase of Linked Genes

Whether linked genes are in cis or trans configuration.

Phenotype

The observable characteristics of an organism.

Pleiotropy

When one gene influences multiple phenotypic traits.

Punnett Square

A diagram used to predict genetic crosses.

Quantitative Traits

Traits influenced by multiple genes and environmental factors.

Recessive

An allele that is only expressed in the homozygous state.

Reciprocal Cross

A cross where male and female traits are reversed.

Recombination

The exchange of genetic material during crossing over.

Recombination Frequency

The percentage of recombinant offspring used to estimate gene distance.

Single Crossover (SCO)

A crossover event between homologous chromosomes.

Sister Chromatid (2)

Identical copies of a chromosome formed during replication. (2)

Syntenic

Genes located on the same chromosome.

Test Cross

A cross with a homozygous recessive individual to determine genotype.

Three-point Test Cross

A genetic cross used to determine gene order and map distances.

True Breeding

Organisms that consistently pass the same traits to offspring.

Variable Expressivity

When individuals with the same genotype show different phenotypic intensities.

Wild Type

The most common phenotype or allele in a population.

X-inactivation

The process of silencing one X chromosome in female mammals.

Xist Gene

A gene responsible for X-inactivation.